Topic 5.1 Cellular respiration

Question 1

Define cellular respiration

Answer 1

the process by which food is broken down to yield ATP, which is used as a source of energy for metabolic reactions

Question 2

What’s the respiratory substrate?

Answer 2

the substance oxidised during cellular respiration

Question 3

Define aerobic respiration

Answer 3

the from of cellular respiration that takes place in the mitochondria in the presence of oxygen

Question 4

What are stalked particles?

Answer 4

structures where ATP production takes place on the inner mitochondrial membranes

Question 5

Define reduction

Answer 5

the addition of electrons to a substance e.g. by the addition of hydrogen or the removal of oxygen

Question 6

Define oxidation

Answer 6

the removal of electrons from a substance e.g. by the addition of oxygen or removal of hydrogen

Question 7

What is a hydrogen acceptor?

Answer 7

a molecule which receives hydrogen and becomes reduced in cell biochemistry

Question 8

What’s NAD?

Answer 8

a coenzyme that acts as a hydrogen acceptor

Question 9

What’s reduced NAD?

Answer 9

NAD which has accepted a hydrogen atom in a metabolic pathway

Question 10

What is glycolysis?

Answer 10

the first stage in cellular respiration, which takes place in the cytoplasm and is common to both aerobic and anaerobic respiration

Question 11

What is pyruvate?

Answer 11

the end-product of glycolysis

Question 12

What’s the purpose of aerobic respiration?

Answer 12

• produces ATP, which can be hydrolysed to ADP and Pi

- releases energy for metabolic reactions/ phsophoylate compounds to make them more reactive

Question 13

Name the 4 main stages of aerobic respiration and where they occur

Answer 13

Glycolysis- cytoplasm
Link reaction- matrix of mitochondria
Krebs cycle- matrix of mitochondria
Electron transport chain- membrane of cristae

Question 14

Outline the stages of glycolysis

Answer 14

1. glucose is phosphorylated using ATP by adding 2 phosphate groups (phosphorylated sugar is more reactive and unable to pass through the cell membrane)
2. phosphorylated sugar is split into 2 x 3C sugar glycerate-3-phosphate (GP)
3. 2 x GP converted into 2 x pyruvate (3C), NAD to NADH by hydrogen atoms from GP- 4x ATP molecules produced. phosphorylation of sugar reversed and pi used to convert ADP-> ATP
   net gain of 2x reduced NAD and 2x ATP per glucose

Question 15

How does pyruvate from glycolysis enter the mitochondria?

Answer 15

via active transport

Question 16

What happens during the link reaction?

Answer 16

1. pyruvate crosses the mitochondrial membrane and enters the mitochondria
2. pyruvate is decarboxylated by decarboxylases and a molecule of CO2 is produced
3. the 2C compound joins with coenzyme A to form acetyl coenzyme A
4. at the same time pyruvate is oxidised, losing hydrogens to NAD which results in NADH (NADH used later in ETC)
5. energy contained in the acetyl coenzyme A is released into the Krebs cycle

Question 17

Give a summary equation for a link reaction

Answer 17

pyruvate + NAD + CoA —> acetyl CoA + reduced NAD + CO2

Question 18

What happens in the Krebs cycle?

Answer 18

1. oxaloacetic acid (4C) combines with acetyl coenzyme A (2C) to form citrate (6C)
2. citrate is decarboxylated so CO2 is given off and oxidised which means NAD is reduced to NADH to form a 5C compound
3. the 5C compound gets decarboxylated, oxidised (which reduces 2 x NAD to NADH and 1 x FAD to FADH2) and phosphorylated which produces ATP from ATP. this forms oxaloacetic (4C) acid again

Question 19

What is the electron transport chain?

Answer 19

a series of carrier proteins embedded in the membrane of the cristae in the mitochondria

Question 20

What is the process the ETC uses to produce ATP in aerobic respiration?

Answer 20

oxidative phosphorylation via chemiosmosis

Question 21

What happens in the electron transport chain?

Answer 21

• electrons released from NAD and FAD undergo redox reactions (NADH and FADH2 are oxidised)
• energy released is coupled in maintaining proton gradient (H+) or released as heat
• oxygen acts as final electron acceptor

Question 22

How is the H+ gradient established during chemiosmosis in aerobic respiration?

Answer 22

some energy released in the ETC is used to actively transport H+ ions from the mitochondrial matrix to the intermembrane space

Question 23

How does chemiosmosis produce ATP?

Answer 23

H+ ions move down the concentration gradient via ATP synthase (channel protein) from the intermembrane space to the matrix
ATP synthase catalyses ADP + PI —> ATP

Question 24

What’s the role of oxygen in the ETC?

Answer 24

final electron acceptor (produces water)

Question 25

State the benefit of an ETC instead of a singe reaction

Answer 25

• energy is released gradually

- less energy released as heat

Question 26

What is anaerobic respiration?

Answer 26

form of cellular respiration, takes place only in the cytoplasm when there is no oxygen present

Question 27

State the stages of anaerobic respiration

Answer 27

1) Glycolysis: glucose is phosphorylated using ATP to add 2 phosphate groups. it is then split to form 2 x glycerate 3-phosphate (GP), a 3 C sugar. GP is then converted in multiple steps into pyruvic acid.
net gain of 2 ATP molecules
2) pyruvate from glycolysis is converted into lactic acid

Question 28

Explain the role of the Krebs cycle

Answer 28

• completely oxidises pyruvate/acetyl Co A
• to release as much energy as possible
• to generate ATP
• to produce reduced coenzyme/NADH
• so that ATP can be produced in the ETC/by oxidative phosphorylation

Question 29

How many molecules of NADH, FADH2 and ATP are produced from one molecule of pyruvate going through the krebs cycle?

Answer 29

3 x NADH
1 x FADH2
1 x ATP